Heretofore, in adjusting an output of a laser beam oscillated from a laser oscillator, an intensity of the laser beam oscillated from the laser oscillator is measured using a laser output measuring apparatus.
FIG. 12 is a configuration diagram showing a conventional laser output measuring apparatus disclosed in the following Patent Document 1.
As shown in FIG. 12, the conventional laser output measuring apparatus is configured with an optical separator 102 that reflects a part of a laser beam emitted from a laser oscillator 101 as a monitoring beam, and a photodetector 103 that detects an intensity of a reflected beam from the optical separator 102.
The intensity measured by the photodetector 103 is fed back to the laser oscillator 101, and the output of the laser beam is adjusted according to a measurement result of the intensity.
On the other hand, the laser beam transmitted through the optical separator 102 is used for an original purpose of the laser beam.
In this case, the optical separator 102 is disposed in a state inclined at a predetermined angle (usually, inclined at 45°) with respect to a direction of an optical axis 104 of the laser beam emitted from the laser oscillator 101.
Further, in order for a reflection surface of the optical separator 102 to have an intended reflectivity, a partially reflective coating of a dielectric multilayer film is usually applied thereon.
Since the partially reflective coating serves to reflect the part of the laser beam for the purpose of measuring an intensity of the laser beam, it is usually the coating in a low reflectivity region.
The dielectric film of the partially reflective coating has a property in which the reflectivity changes due to absorption of atmospheric moisture or due to temperature.
For example, when the optical separator 102 of 1% in reflectivity (99% in transmission) is used, a change of 0.1% in reflectivity results in an output change of 10% (=0.1%/1.0%) in the output change of the laser beam reflected by the optical separator 102.
Accordingly, even though deterioration occurs in the dielectric film of the partially reflective coating, and the reflectivity thereof varies slightly, a large output change in the reflected laser beam occurs.
Incidentally, the following is known: it is difficult to control a dielectric film having a low reflectivity, so that a large variation thereof occurs, and also the formation of the film is costly.
In the conventional laser output measuring apparatus, the photodetector 103 detects the intensity of the laser beam reflected by the optical separator 102 as mentioned above; however, when the laser beam emitted from the laser oscillator 101 enters the optical separator 102, an incident angle of the laser beam differs depending on an incident position thereon, so that the reflectivity of the laser beam reflected by the optical separator 102 differs depending on the incident position. For this reason, it is difficult to measure accurately the output of the laser beam emitted from the laser oscillator 101.
Thus, instead of the dielectric multilayer involving a larger variation in reflectivity depending on the incident angle, a method that applies a coating of a metal film on the reflection surface of the optical separator 102 is considered; however, even in this case, the formation of the film is costly, which makes the laser output measuring apparatus expensive.